Matti Lehtonen

Bio: Matti Lehtonen is an academic researcher from Aalto University. The author has contributed to research in topics: Fault (power engineering) & Electric power system. The author has an hindex of 40, co-authored 694 publications receiving 8559 citations. Previous affiliations of Matti Lehtonen include Razi University & New York University.

A General Framework for Voltage Sag Performance Analysis of Distribution Networks

Abstract: The proliferation of more sensitive loads has obliged distribution companies to pay greater attention to the voltage sag mitigation potential of different design alternatives in network planning studies. In doing so, a company has to have effective tools for estimating the voltage sag performance of its network. In this regard, this paper establishes a three-step framework for evaluating voltage sag performance of a distribution network. The first step, designated as state selection, is to select a network state in which voltage sag is likely. Although voltage sags have various causes, those that originated from faults in distribution networks are considered in this paper. The stochastic nature of fault location, type, resistance, and duration as well as the response of the protection system are taken into account. The second step, called state evaluation, deals with sag characteristics during the fault clearing time and the protection system response. The third step, named index calculation, is to estimate indices reflecting the sag performance of the network. A number of indices are proposed in this paper to reflect both system and load point-oriented issues. In light of the indices, companies may find effective solutions for voltage sag mitigation and customers choose appropriate solutions to provide ride-through support for their critical processes.

Experimental verification of distribution transformer model under lightning strokes

Abstract: In this paper, the distribution transformer model under lightning impulses introduced by Piantini at no load conditions is investigated This model is modified where this modification takes more than one resonance frequency into consideration during the model parameters calculation Therefore, the frequency response of the simulated transient voltage is improved comparing with Piantini model The verification of the modified model is carried out through the comparison between the experimental and simulation results, in which the time domain simulation is carried out using ATP/EMTP while MATLAB is used to identify the model parameters The comparison showed a good agreement between the simulation and experimental results

An integrated solution for protection and automation of power systems

Abstract: The paper presents an integrated solution for power system protection and medium voltage network and substation automation. For network automation, the remote control and monitoring of sectionalizing and tie switches is discussed. With regard to the substation automation, the integration of numeric protective relays into the substation telecontrol system (SCADA) is studied. A solution is presented, where the protective relays are connected to the station computer via a fibre optic based local area network. The station computer, in turn, works as a remote terminal unit of the telecontrol system. An advanced solution is presented for the integration of the telecontrol system and the distribution data management system (DMS). Here the data communication works two-ways. From the operator's point of view, the system appears as one entity. The telecontrol system is responsible for the control commands and on-line measurements. The role of DMS is to display the network topology and to analyse the network condition by various calculations. To illustrate the operation of the integrated automation system, the applications for fault location and supply restoration are presented in more detail. The fault location is based on two different solutions. By computational means it is possible to produce an estimate for the fault distance from the substation. This function is based on an analysis of fault currents recorded by the numerical relays at the substation. Since there usually are many line branches, the computational means also yield several possible fault locations. In order to find the actual fault location, the remote reading of the fault indicators, mounted at the disconnector stations, is used. Finally the function for automatic fault isolation and fault restoration is discussed. This application is based on the remote control of line switches by the telecontrol system, combined with the topology analysis and fault location analysis in the DMS system.

Evaluating and improving the energy efficiency of counterbalanced elevators based on passenger traffic

Abstract: Passenger traffic has been widely neglected when considering the elevator energy consumption. Earlier, the consumption has been typically estimated in the design phase of the building by a simple energy per square meter approach. Recently, energy efficiency classification schemes for elevators, VDI 4707-1 and ISO 25745-2, have presented computational methods applying reference power measurements from the installation site to determine specific energy usage categories and to provide an estimate of annual consumption. The ratio of standby and running energy demand are based on the building type related to a certain number of starts per day. The usage of the elevator directly derives from the passenger traffic profile. Therefore, this paper highlights the importance of analyzing the passenger flow, car loading in each direction, length of trips, and their impact on the elevator energy consumption. The modeled results of the case building imply that a substantial share of the total electricity consumption is related to other forms than transporting the passengers between floors. The main cause is considered to be the low average loading in contrast to a commonly used heavy counterbalance. Thus, the paper suggests measures to decrease the energy consumption by resizing the counterbalance and compares the results to regenerative solutions. When the counterbalance is sized optimally, the modeled efficiency improvement of the counterbalance resizing nearly equals the regenerative system with approximately 60% total savings in the case office building.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

The Design and Analysis of Experiments

Abstract: THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

World energy outlook

Abstract: This chapter discusses leading problems linked to energy that the world is now confronting and to propose some ideas concerning possible solutions. Oil deserves special attention among all energy sources. Since the beginning of 1981, it has merely been continuing and enhancing the downward movement in consumption and prices caused by excessive rises, especially for light crudes such as those from Africa, and the slowing down of worldwide economic growth. Densely-populated oil-producing countries need to produce to live, to pay for their food and their equipment. If the economic growth of the industrialized countries were to be 4%, even if investment in the rational use of energy were pushed to the limit and the development of nonpetroleum energy sources were also pursued actively, it would be extremely difficult to prevent a sharp rise in prices. It is evident that it is absolutely necessary to pursue actively the development of coal, natural gas, and nuclear power if a physical shortage of energy is not to block economic growth.